Java 8 新特性:6-Optional类

 先看看上面的说明： 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 /**   * A container object which may or may not contain a non-null value.   * If a value is present, {@code isPresent()} will return {@code true

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